Many PoE customers want more power for a PD than the current IEEE standards allow. Some of these customers also want to remain fully compliant with the IEEE 802.3 PoE specification. The IEEE 802.3 specification is incorporated herein by reference. For these customers, the only way to get more power using PoE is to combine the power from two or more IEEE 802.3 compliant Power Sourcing Equipment (PSE) PoE channels, such as combining the power supplied through two or more Ethernet cables carrying PoE, to power a single PD.
The traditional method of combining the power from multiple PSE channels is for each PSE channel to have a corresponding PD interface controller and an isolated PD Power Supply (PDPS), where the outputs of all the PDPS's are connected in parallel and to the single PD load. Each of the PSE channels supply the standard voltage, such as 44-57 volts, to the proper pairs of cables in their associated Ethernet cable in accordance to the IEEE PoE specifications. On the PD side, the voltage from each PSE channel is DC-DC converted by separate isolated power supplies (the PDPS's) to the desired voltage needed by the single PD load. All of the PDPS's are then designed so that each one supplies an equal share of the total load current. This necessitates communication between all of the PDPS's. For example, one PDPS may act as the master and another PDPS may act as a slave. The master then controls the slave to operate synchronously with the master to supply one half of the current to the single PD load at a regulated voltage. The power supplies on the PSE side (supplying 44-57 volts) may, optionally, also communicate with each other.
Syncing two or more PDPS's together to supply equal power adds complexity and limits the types of PDPS's that can be used in an Ethernet system.
Therefore, what is needed is a technique for two or more PDPS's to combine their power for a single PD load when the PD load requires more power than one PDPS can supply, where the PDPS's do not have to be synchronized to provide their combined power to the PD load.